Field of the Invention
The present invention relates to a bump electrode, a board which has bump electrodes and a method for manufacturing the board. It particularly relates to a bump electrode formed by using a solder joint in which a core material that becomes a core is covered with solder plating, a board such as semiconductor chip or printed circuit board which has bump electrodes (hereinafter, referred to as “board which has bump electrodes), and the method for manufacturing the board.
Description of Related Art
Recently, a rapid downsizing of electronic components to be mounted on small sized information equipment such as a smart phone has been required because of a development of the small sized information equipment. On such electronic components, ball grid array (hereinafter, referred to as “BGA”) in which an array of small ball electrodes is arranged on a plane resin-made package is applied because of a narrowed connection terminal based on the requirement of the downsizing, a fine pitch between the electrodes and/or a reduction of mounting area.
As electronic components on which BGA is applied, the semiconductor package such as central processing unit (CPU) is represented. In the semiconductor package, a semiconductor chip having plural electrodes is sealed with resin. For each electrode in the semiconductor chip, a solder bump is formed. Such a solder bump is formed by joining a solder ball made by forming a solder like a ball with an electrode of the semiconductor chip.
The semiconductor package on which BGA is applied is mounted on a printed circuit board by joining the solder bump melted by heating with a conductive land (electrode pad) of the printed circuit board.
Any three-dimensional layered structures in each of which the semiconductor packages are stacked in height direction thereof have been developed, to cope with a requirement of further high density mounting. However, when BGA is applied on the semiconductor packages having such a three-dimensional layered structure, the solder ball may be crushed by the upper semiconductor-package's weight. The crushed solder ball may be pushed out of an electrode of connecting terminal and such an electrode may be connected with adjacent electrode to be short-circuited.
Accordingly, a bump electrode as the electrode for electronic components has been used. The bump electrode is referred to as an electrode that is made by using a Cu core ball in which a core material, for example, Cu ball that becomes a core is covered with plated Ni and the Ni-plated core material is then covered with solder plating. The bump electrodes each made by using the core material can support the upper semiconductor package by Cu balls which are not melted at a melting point of the solder even if weight of the upper semiconductor package is applied to the bump electrodes when mounting the electronic components on the printed circuit board. Thus, the bump electrodes are not crushed by the weight of the upper semiconductor package.
On the other hand, in the past, a reflow furnace has been used when soldering the electronic components on predetermined positions of the printed circuit board. Flux or solder paste has been used when forming the bump electrodes in the reflow furnace. The solder paste is made by stirring solder powder with flux. The flux, solder paste or the like is applied on plural electrode pads formed on a substrate, on which a metal mask is aligned and a squeegee is slid on the metal mask, through plural holes formed in the metal mask. The other applying method of the flux, solder paste or the like than that of directly applying them on the electrode pads using the metal mask can be adopted. For example, their applying methods include a ball transfer method, a pin transfer method, a dispense method and a splay method.
The flux removes any oxide film from a metal surface to be soldered and prevents the metal surface from being again oxidized during a period of heating time in a soldering step. The flux has an action of reducing surface tension of the solder and improving wettability thereof. The flux is a solution made by melting solid contents of rosin, thixotropic agent, activator or the like using a solvent.
Japanese Patent Appiication Publication No. 2006-344624 discloses a method of manufacturing an electronic component. This method includes arranging Cu-cored solder ball having a diameter of 0.01 mm through 1 mm on an electrode pad and heating to join them to obtain an electrode that becomes a connecting terminal.
When this Cu-cored solder ball also has a relation of 0.05≦(Vs/Vc)≦0.5 wherein Vc is volume of the Cu-cored solder ball and Vs is volume of plated layer and this electrode pad has a relation of 0.5≦(Dp/Dc0)≦1.0 wherein Dp is a diameter of the electrode pad and Dc is a diameter of the Cu-cored solder ball, the core is positioned at a center of the electrode pad.